1. Field of the Invention
The present invention relates to a lens barrel having an optical element, which is positioned on the optical axis in a ready-to-photograph state, and which also is removed from the optical axis in an accommodated state.
2. Description of the Related Art
In a known type of lens barrel in which the length thereof is made shorter in the optical axis direction when the lens barrel is in an accommodated state, in order to achieve a shorter barrel length, a lens barrel in which the imaging optical system thereof includes a removable optical element (radially-removable optical element) has been proposed. When this known type of lens barrel is in a ready-to-photograph state, the removable optical element is positioned on the optical axis, and when the lens barrel is in the accommodated state, the removable optical element is removed from the optical axis and carries out the accommodating operation. This lens barrel is disclosed in Japanese patent No. 3,771,909. Furthermore, the inventor has also proposed an evacuation mechanism that prevents interference of the removable optical element with other optical elements during accommodating operation of this type of lens barrel. This evacuation mechanism is disclosed in Japanese patent No. 4,520,171.
According to Japanese patent No. 4,520,171, an off-axis removable member that holds a removable optical element is provided, and a rear movable member that holds a rear optical element which is positioned at the rear of the removable optical element in the ready-to-photograph state is also provided. Each of these movable members (the off-axis removable member and the rear movable member) is provided with a contact surface capable of coming in contact with each other in an area other than that of each optical element. When the accommodating operation is carried out in a state wherein the rear movable member is positioned at any position that is closer to the front end of the lens barrel than a predetermined accommodating position in the optical axis direction, via the mutual contact of these contact surfaces, interference between the rear optical element and the off-axis removable member is prevented, and also interference of between the removable optical element and the rear movable member is prevented. In other words, the removing operation of the removable optical element is carried out by direct contact of these movable members that respectively hold the optical elements. However, the off-axis removable member, which holds the removable optical element, needs a more strict and accurate product quality control than the other holding (movable) members for ordinary optical elements that simply move in the optical axis direction only. Therefore, it is desirable for the load on the off-axis removable member to be as small as possible.